code: def test_introduce_remark():
      """Test introducing a REMARK entry to the file with no remarks."""
      # Add remark
      code = 3
      remark = "THIS IS A HIGHLY IMPORTANT FREE-TEXT REMARK WHICH IS EXACTLY 80 CHARACTERS LONG."
      indent = 1
      ppdb = PandasPdb()
      ppdb.read_pdb(TESTDATA_FILENAME3)
      n_atoms = len(ppdb.df["ATOM"])
      ppdb.add_remark(code, remark, indent)
      ppdb.to_pdb(path=OUTFILE)
  
      # Test modified file starts with new remark
      with open(OUTFILE, "r") as f:
          f1 = f.read()
      expected_prefix = (
          "REMARK   3  THIS IS A HIGHLY IMPORTANT FREE-TEXT REMARK WHICH IS EXACTLY 80     \n"
          "REMARK   3  CHARACTERS LONG.                                                    \n"
      )
      assert f1.startswith(expected_prefix)
  
      # Test number of atoms remained the same
      ppdb = PandasPdb()
      ppdb.read_pdb(OUTFILE)
      os.remove(OUTFILE)
      assert len(ppdb.df["ATOM"]) == n_atoms
  
file_path: biopandas/biopandas/pdb/tests/test_write_pdb.py
imports: from biopandas.pdb import PandasPdb
  import warnings
  import pandas
  import os
label_desc: Use image node_id 6 for calling a global function with example usage: test_introduce_remark() without return types